Doubly salient permanent magnet electric machine

ABSTRACT

Disclosed herein is a linear, curved or rotary electric machine. The electric machine includes first and second movers which are adjacent to each other and have a phase angle difference of 60° therebetween. The first mover includes phases U, V and W and the second mover includes phases /U, /V and /W. The electric machine of the present invention can reduce pulsations of thrust caused by end effect. In particular, in the case where the stator includes permanent magnets having the same poles and salient poles which alternate with the permanent magnets, the number of permanent magnets used can be reduced to half of that of a conventional linear electric machine.

CROSS-REFERENCES

The present application is a continuation application of U.S. patentapplication Ser. No. 12/796,846 filed on Jun. 9, 2010, which claimspriority to Korean Patent Application No. 10-2009-0059011 filed on Jun.30, 2009, which are incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to linear, curved or rotaryelectric machines and, more particularly, to an electric machine whichincludes first and second movers which are adjacent to each other andhave a phase angle difference of 60° therebetween, wherein when thefirst mover includes phases U, V and W and the second mover includesphases /U, /V and /W, pulsations of thrust caused by end effect can bemitigated, and when a stator comprises an iron core having permanentmagnets and salient poles which alternate with each other, the number ofpermanent magnets can be reduced to half of that of a conventionallinear electric machine.

2. Description of the Related Art

Generally, linear electric machines have been widely used for precisionposition control. A permanent magnet linear synchronous motor is arepresentative example of such conventional linear electric machines.Typically, in a conventional permanent magnet linear synchronous motor,a mover includes an iron core and three-phase coils, and a statorincludes an iron core and permanent magnets. Therefore, as the distancethat the mover moves is increased, the number of permanent magnets usedis increased, resulting in an increase in the production cost. Inaddition, due to end effect induced on an entry end and an exit end ofthe mover, there is pulsation of thrust and normal force.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made keeping in mind theabove problems occurring in the prior art, and an object of the presentinvention is to provide an electric machine in which a stator comprisesan iron core having permanent magnets and salient poles which alternatewith each other, thus reducing the number of permanent magnets used,compared to the conventional linear electric machine, and which includesfirst and second movers which have phase angle difference of 60°, thusreducing pulsations of thrust and normal force.

Another object of the present invention is to provide an electricmachine which can have various structures which are required of appliedsystems, for example, in which stators are disposed on opposite sides ofa mover or movers are disposed on opposite sides of a stator, such thatattractive force between the stator and the mover can be canceled.

In order to accomplish the above object, the present invention providesan electric machine which is provided with a pair of movers which havean electrical phase difference of 60°, thus reducing pulsations ofthrust.

Furthermore, a stator may comprise an iron core having permanent magnetsand salient poles which alternate with each other. Thus, the number ofpermanent magnets used can be reduced compared to that of theconventional permanent magnet linear synchronous motor.

Each of the pair of movers may include mover teeth in the quantity of amultiple of three which are arranged at regular intervals (α) withrespect to the direction in which the movers move, and coils woundaround the mover teeth.

In addition, the stator and the mover may be configured such that thesalient poles of the stator and the corresponding mover teeth of themover are skewed at predetermined angles and face each other.

Moreover, the electric machine may be configured such that statorshaving permanent magnets and salient poles are disposed on oppositesides of a mover or the same number of movers are disposed on oppositesides of a stator, such that attractive force between the stator and themover can be canceled.

The electric machine may have an air core type structure such thatstators having permanent magnets and salient poles are disposed atpositions opposite to each other and three-phase coils are providedbetween the stators.

In detail, in an aspect, the present invention provides an electricmachine, including: a stator; and a plurality of movers arranged atpositions spaced apart from each other such that an electric phasedifference therebetween is 60° or 180°. The movers linearly or curvedlymove or rotate with respect to the stator. Each of the movers includes:mover teeth in multiples of three, the mover teeth being spaced apartfrom each other at regular intervals; and a phase coil wound around eachof the mover teeth. The stator comprises an iron core having a pluralityof salient poles. Permanent magnets are provided in depressions definedbetween the salient poles.

In another aspect, the present invention provides an electric machine,including: a stator; and a plurality of movers arranged at positionsspaced apart from each other such that an electric phase differencetherebetween is 60° or 180°. The movers linearly or curvedly move orrotate with respect to the stator. Each of the movers includes: moverteeth in multiples of three, the mover teeth being spaced apart fromeach other at regular intervals; and a phase coil wound around each ofthe mover teeth. The stator comprises a linear iron core. A plurality ofpermanent magnets is provided on the iron core. The permanent magnetsare arranged such that opposite poles of the adjacent permanent magnetsface each other.

In a further aspect, the present invention provides an electric machine,including: two stators; and a mover provided between the two stators,the mover linearly or curvedly moving or rotating with respect to thestators. The mover includes: mover teeth in multiples of three providedon each of opposite surfaces of the mover which face the two stators,the mover teeth being arranged at positions spaced apart from each otherat regular intervals; and a phase coil wound around each of the moverteeth. Each of the two stators comprises an iron core. A plurality ofsalient poles is provided on a surface of the iron core facing themover. Permanent magnets are provided in depressions defined between thesalient poles, so that attractive force between the stators and themover is canceled.

In yet another aspect, the present invention provides an electricmachine, including: a stator; and two movers provided on opposite sidesof the stator such that the two movers face each other, each of the twomovers linearly or curvedly moving or rotating with respect to thestator. Each of the movers has on a surface thereof facing the stator:mover teeth in multiples of three, the mover teeth being spaced apartfrom each other at regular intervals; and a phase coil wound around eachof the mover teeth. The stator comprises an iron core. A plurality ofsalient poles is provided on each of opposite surfaces of the iron corefacing the movers, and permanent magnets are provided in depressionsdefined between the salient poles, so that attractive force between thestator and the movers is canceled.

The salient poles of the stator and the corresponding mover teeth of themover may be skewed at predetermined angles and face each other.

The mover may comprise a plurality of movers each of which has moverteeth in multiples of three, and an electric phase difference betweenthe movers may be 60° or 180°.

The movers may be mechanically integrated with each other by anintegrated common iron core.

The phase coils of the first mover of the plurality of movers may havean electrical phase difference of 180° with respect to one of the phasecoils of the second mover of the plurality of movers.

In still another aspect, the present invention provides an electricmachine, including: at least one stator; and a mover linearly orcurvedly moving or rotating with respect to the stator. The statorcomprises an iron core. A plurality of salient poles is provided on asurface of the iron core facing the mover. Permanent magnets areprovided in depressions defined between the salient poles. The movercomprises three-phase coils or phase coils configured such thatthree-phase coils are repeated in a direction in which the mover moves.

The stator may comprise two stators, and the mover may be providedbetween the two stators. Each of the two stators may have, on a surfacethereof facing the mover, permanent magnets provided in depressionsdefined between the salient poles.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be more clearly understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a view illustrating a mover and a stator of a linear electricmachine, according to a first embodiment of the present invention;

FIG. 2 is a view illustrating a mover and a stator of a linear electricmachine, according to a second embodiment of the present invention;

FIG. 3 is a view showing the construction of a conventional linearelectric machine;

FIG. 4 is a view illustrating a linear electric machine in which twostators having permanent magnets and salient poles are disposed onopposite sides of a single mover to cancel the attractive forcetherebetween, according to a third embodiment of the present invention;

FIG. 5 is a view illustrating a linear electric machine in which twomovers are disposed on opposite sides of a stator on each of bothsurfaces of which there are permanent magnets and salient poles tocancel the attractive force therebetween, according to a fourthembodiment of the present invention;

FIG. 6 is a view illustrating a linear electric machine in which twostators having permanent magnets and salient poles are disposed oppositeto each other and an air core type mover having three-phase coils isdisposed between the stators, according to a fourth embodiment of thepresent invention;

FIG. 7 is a graph analytically comparing thrust of linear electricmachines proposed in conventional techniques and the present invention;and

FIG. 8 is a graph analytically comparing the attractive force of linearelectric machines proposed in conventional techniques and the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the attached drawings, but thepresent invention is not limited to the embodiments and variousmodifications are possible using a combination of the embodiments.Furthermore, reference now should be made to the drawings, in which thesame reference numerals are used throughout the different drawings todesignate the same or similar components.

Electric machines described in the present invention are energyconversion devices which convert electric energy into kinetic energy orconvert kinetic energy into electric energy, for example, including amotor, an actuator and a generator. In addition, the electric machinesmean devices which implement the above-mentioned energy conversion usinglinear motion, rotation or a combination of linear motion and rotation.

FIG. 1 is a view illustrating the general construction of a linearelectric machine and disposition of a first mover A and a second mover Bwhich linearly move with respect to a stator 2, according to a firstembodiment of the present invention. The first mover A and the secondmover B are spaced apart from each other by β (an electrical phase angleof 60°=τ_(p)/3, τ_(p) denotes a pole pitch). The first mover A includesphases U, V and W. The second mover B includes phases /U, /V and /W.Phase coils 1 b of each of the first and second movers A and B are woundparallel to each other at regular intervals α, for example, such that adifference between electrical phase angles of the adjacent phase coils 1b becomes 120°. Here, the order of the phases /U, /V and /W of thesecond mover B is not unconditional. In other words, depending on thenumber of poles or the number of mover teeth 1 a (for example, amultiple of three), the order of the phases /U, /V and /W may vary.Preferably, regardless of the order of coils, the phases /U, /V and /Wof the phases coils 1 b of the second mover B are arranged such that thephases /U, /V and /W have electrical phase differences of 180° withrespect to the phases U, V and W of the phase coils of the first moverA. Here, ‘/U’ denotes a phase difference of 180° with respect to thephase U. ‘/V’ denotes a phase difference of 180° with respect to phaseV. ‘/W’ denotes a phase difference of 180° with respect to phase W.

Each of the first and second movers A and B (1) has phase coils 1 bwhich have electrical phase differences of 180°. Hence, when necessary,β may be changed into an electrical phase angle of 180° (τ_(p)).

In FIG. 1, although the first and second movers A and B (1) have beenillustrated as being mechanically separated from each other, the presentinvention is not limited thereto. For example, a pair of movers A and Bmay be configured such that they are integrated with each other using anintegrated iron core. In this case, mover teeth present in a multiple ofthree (for example, six mover teeth) are provided, and phase coils areprovided on the six mover teeth having phases U, V, W, /U, /V and /W.

Furthermore, although the structure having the two movers A and B (1)has been illustrated as an example, one or more movers may be furtherprovided, in other words, three or more movers may be provided. Ofcourse, in this case, the three or more movers may be spaced apart fromeach other such that electrical phase differences of 60° or 180°therebetween exist, or they may be integrated with each other using anintegrated iron core. Here, phase coils having phases U, V, W, /U, /Vand /W may be repeatedly provided on mover teeth in multiples of three.In addition, each mover may have mover teeth in multiples of three. Inthis case, of course, the number of all mover teeth of three or moremovers is a multiple of three.

As shown in FIG. 1, in the linear electric machine according to theembodiment of the present invention, the stator 2 has an iron coreprovided with stator salient poles 2 b. Permanent magnets 2 a areprovided in depressions defined between the stator salient poles 2 b.That is, the permanent magnets 2 a and the stator salient poles 2 balternate on the iron core of the stator 2.

FIG. 2 is a view illustrating a linear electric machine, according to asecond embodiment of the present invention. The construction of twomovers A and B is the same as that of the linear electric machine ofFIG. 1, but in the embodiment of FIG. 2, the stator 2 includes onlypermanent magnets 2 a and an iron core. In other words, in the linearelectric machine according to the second embodiment, the stator 2 isconfigured such that permanent magnets 2 a are provided on a linearstator iron core without having stator salient poles. Here, thepermanent magnets 2 a are arranged such that opposite poles of adjacentmagnets 2 a face each other.

FIG. 3 is a view showing the construction of a conventional linearelectric machine. In the conventional linear electric machine, a moverincludes mover iron cores 1 a which are mover teeth in multiples ofthree. Phase coils 1 b having phases of U, V and W are repeatedlyprovided on the mover iron cores 1 a. In a stator 2, permanent magnets 2a are provided on a linear stator iron core without having statorsalient poles, in the same manner as that of FIG. 2. Furthermore, thepermanent magnets 2 a are arranged such that opposite poles of adjacentmagnets 2 a face each other. However, in the construction of theconventional linear electric machine, as the movement distance of themover increases, the number of required permanent magnets increases,thus resulting in an increased production cost. Furthermore, due to theend effect induced on an entry end and an exit end of the mover,pulsations of thrust and normal force are caused. Therefore, thisconventional technique is not suitable for precision position control.

FIG. 4 is a view illustrating a linear electric machine, according to athird embodiment of the present invention. As shown in FIG. 4, thelinear electric machine according to the third embodiment includes amover 1 and two stators 2. The two stators 2 are disposed on oppositesides of the mover 1 with respect to a direction perpendicular to thedirection in which the mover 1 moves. Permanent magnets 2 a and statorsalient poles 2 b are provided on a surface of each stator 2 which facesthe mover 1. Due to this structure, attractive force between the mover 1and the two stators 2 can be canceled. Here, the mover 1 is configuredsuch that mover teeth 1 a in multiples of three are provided on each ofthe opposite sides of the mover 1 which face the two stators 2 andthree-phase coils 1 b are provided on the mover teeth 1 a in a mannersimilar to that of FIG. 3. Furthermore, the mover 1 may comprise two ormore movers which are configured such that phase coils having phases U,V, W, /U, /V and /W are repeatedly provided on each of opposite sides ofthe movers which have electrical phase differences of 60° or 180° in amanner similar to that of FIG. 1. Preferably, the two stators 2 whichare opposite to each other are disposed such that the permanent magnets2 a of one stator 2 face the stator salient poles 2 b of the otherstator 2.

FIG. 5 is a view illustrating a linear electric machine, according to afourth embodiment of the present invention. As shown in FIG. 5, twomovers 1 are disposed at positions opposite to each other. A stator 2 isdisposed between the two movers 1. Permanent magnets 2 a and statorsalient poles 2 b which have the structure similar to those of FIG. 1are provided on each of both surfaces of the stator 2 which faces themovers 1 with respect to the direction perpendicular to the direction inwhich the movers 1 move. Due to this structure, attractive force betweenthe movers 1 and the stator 2 can be canceled. This embodiment isconfigured such that the mover 1 which has three-phase coils 1 b in thesame manner as that of the mover 1 of FIG. 3 is provided on each ofopposite sides of the stator 2. Each of the movers 1 which are disposedon opposite sides of the stator 1 may comprise two or more movers whichare configured such that phase coils having phases U, V, W, /U, /V and/W are repeatedly provided on the movers which have electrical phasedifferences of 60° or 180° in a manner similar to that of FIG. 1.Furthermore, with regard to the arrangement of the permanent magnets 2 aand the stator salient poles 2 b provided on both surfaces of the stator2, it may be configured such that the permanent magnets 2 a are providedon one surface of the stator 2 and the stator salient poles 2 b areprovided on the other surface of the stator 2.

FIG. 6 is a view illustrating a linear electric machine, according to afifth embodiment of the present invention. As shown in FIG. 6, thelinear electric machine according to the fifth embodiment includes twostators 2 which are disposed at positions opposite to each other. Eachstator 2 has permanent magnets 2 a and stator salient poles 2 b in amanner similar to that of the stator of FIG. 1. A mover is providedbetween the two stators 2. The mover includes phase coils 1 b which areconfigured such that three-phase (U, V, W) coils are provided in theform of an air core, that is, without an iron core, or three-phase coilsare repeatedly provided with respect to the direction in which thatmover moves. Preferably, the two stators 2 which are opposite to eachother are disposed such that the permanent magnets 2 a of one stator 2face the stator salient poles 2 b of the other stator 2. In thisembodiment, although the linear electric machine has been illustrated ashaving two stators 2, only one stator may be disposed on one side of themover or two or more stators may be disposed on each of opposite sidesof the mover.

FIG. 7 is a graph analytically comparing thrust of linear electricmachines proposed in conventional techniques and the present invention,and FIG. 8 is a graph analytically comparing attractive force of linearelectric machines proposed in conventional techniques and the presentinvention. In FIGS. 7 and 8, the conventional design 1 shows the case ofa conventional linear electric machine having the structure of FIG. 3.The conventional design 2 denotes the case where the mover of theconventional linear electric machine of FIG. 3 is combined with the ironcore type stator of FIG. 1 having the stator salient poles. Furthermore,in FIGS. 7 and 8, the proposed design 1 shows the case of FIG. 1 wherethe stator comprises the iron core having the permanent magnets and thestator salient poles and the first mover and the second mover areelectrically spaced apart from each other at an interval of 60°. Theproposed design 2 shows the case of FIG. 2 where the stator includes thepermanent magnets and the linear iron core and the first mover and thesecond mover are electrically spaced apart from each other at aninterval of 60°.

As can be understood from FIGS. 7 and 8, the linear electric machineproposed in the present invention can reduce pulsations of thrust andattractive force, compared to those of the conventional techniques. Inparticular, in the case where the stator proposed in the presentinvention is used in the structure of the conventional linear electricmachine, it is to be understood that the conventional design 2 markedlyincreases pulsations of thrust and attractive force. However, the design1 proposed in the present invention can generate almost the same thrustas that of the conventional technique despite using only half the numberof permanent magnets as does the conventional technique. Furthermore,the proposed design 1 can reduce pulsations of thrust to ⅕ of those ofthe conventional technique and the attractive force by 10%. In addition,the proposed design 2 can generate almost the same thrust as that of theconventional technique and reduce pulsations of thrust by 50%.

As described above, in a linear electric machine according to thepresent invention, a stator includes permanent magnets and statorsalient poles which alternate each other. Thus, the amount of permanentmagnets used can be reduced, compared to the conventional technique.

Furthermore, the linear electric machine includes first and secondmovers which are electrically spaced apart from each other at a phaseangle of 60°, thus reducing pulsations of thrust and normal force. Inaddition, the linear electric machine is configured such that attractiveforce can be canceled in such a way that the movers or stators aredisposed at positions opposite to each other.

Moreover, the structure of the electric machine according to the presentinvention can also be applied to a rotary electric machine.

The linear or rotary electric machine according to the present inventioncan ensure low noise, low vibration, high precision and high thrust.Therefore, the present invention can be used in fields in which directoperation or precision position control is required, or in variousmachines, such as a generator, a compressor, a processing machine, anindustrial electric machine, etc., in which linear or rotary motion isrequired.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the invention.For example, the present invention may be configured such that a statorhas a curved shape and a mover or movers curvedly move along the stator.Furthermore, if the mover of the linear electric machine of the presentinvention is applied to a stator and the stator of the present inventionis applied to a rotor, the present invention can be used as a rotaryelectric machine in which the rotor rotates with respect to the stator.Meanwhile, the terms “mover”, “rotor” and “stator” used in thedescription of the embodiments are relative concepts. In other words,when necessary, the case where the stator may move while the mover orrotor is stationary can fall within the bounds of the present invention.Moreover, the stator or the mover may be configured such that salientpoles of the stator and teeth of the mover are skewed at predeterminedangles and face each other. As such, the bounds of the present inventionare not limited to the above-mentioned embodiments and must be definedby the accompanying claims or the equivalent of the claims.

What is claimed is:
 1. An electric machine, comprising: a stator; twomovers arranged at positions spaced apart from each other and linearlyor curvedly moving or rotating with respect to the stator; and aplurality of phase coils, wherein each of the movers comprises threemover teeth, the mover teeth being spaced apart from each other atregular intervals, wherein the phase coils are each wound around each ofthe mover teeth, the phase coils having phases U, V, W, /V, /W and /U,respectively, and being arranged in the order of the phases U, V, W, /V,/W and /U, wherein the phases /V, /W and /U have a phase difference of180° with respect to the phases V, W and U, respectively, and whereinthe stator comprises a first iron core having a plurality of salientpoles, with a first plurality of permanent magnets provided indepressions defined between the salient poles, or comprises a secondiron core having a second plurality of permanent magnets provided on thesecond iron core, the second plurality of permanent magnets beingarranged such that opposite poles of adjacent permanent magnets faceeach other.
 2. The electric machine as set forth in claim 1, wherein thesalient poles of the stator and corresponding mover teeth of the moversare skewed at predetermined angles and face each other.
 3. The electricmachine as set forth in claim 1, wherein the movers are mechanicallyintegrated with each other by an integrated common iron core.